Anxiety and cognition in female histidine decarboxylase knockout (Hdc−/−) mice

The role of histamine in brain function has been studied using histidine decarboxylase (HDC) deficient male mice. As the effects of HDC deficiency on brain function might be sex-dependent, we behaviorally analyzed Hdc−/− and control female mice. Compared to female control mice, Hdc−/− female mice showed hypoactivity, increased measures of anxiety, impairments in water-maze performance, but enhanced passive avoidance memory retention. Following behavioral testing, arginine vasopression (AVP) immunoreactivity was higher in the dorsal hypothalamus and central and basolateral nuclei of the amygdala of Hdc−/− than Hdc+/+ mice. Finally, MAP2 immunoreactivity in the hippocampal CA1 region correlated positively with measures of anxiety in the open-field and light–dark tests and negatively with performance during the hidden sessions of the water-maze. As the effects of HDC deficiency on object recognition, water-maze, and rotorod performance, were sex-dependent, it is important to consider potential effects of sex in the interpretation of the role of histaminergic neurotransmission in brain function.